1. Field of the Invention
This invention relates to adjustable down-hole tools employed in the oil and gas drilling industry.
2. Description of the Related Art
Drill string stabilisers, under reamers and fishing tools are some of the down hole tools that require activation when they are in a given position down hole to make them operative, and deactivation when they are to be withdrawn, or repositioned or indeed simply to go into a different operating condition.
Taking stabilisers as an example, these tools centralise drill strings with respect to the hole drilled. They normally comprise a sub assembly in the drill string. The stabiliser has a plurality of blades, (usually three and usually spirally arranged), whose edges are adapted to bear against the bore-hole. The blades are not complete around a circumference of the drill string so that the return route for drilling mud pumped down the bore of the drill string is not blocked. In order to control the direction of drill bits, it is sometimes required that the stabiliser has variable diameter. Pistons in the blades are extendable to give the stabiliser a maximum diameter, which ensures that the drill string is central in the bore-hole. The drill bit, assuming the stabiliser is close behind the drill bit, is thus kept straight. However, if the pistons are withdrawn, then gravity can deflect the drill string so that it alters the inclination of the hole.
EP-A-0251543 describes a slabiliser that is activated by weight on the stabiliser from the drill string above it. Weight, or absence thereof, switches the stabiliser between activated and de-activated positions. The weight acts on a mandrel slidable in the bore of the stabiliser, which mandrel has ramps against which wedge-surfaces on the bases of the pistons slide. A mechanical detent is overcome by a compressive force on the stabiliser greater than a threshold value, so that unless substantial changes in weight act on the stabiliser, switching does not occur. This means that some variation in weight is permissable without changing the activation of the stabiliser. However, it is known that excessive changes in weight can occur unintentionally, possibly resulting in accidental activation and deactivation of the stabiliser.
It has been suggested to employ a rise in mud pump pressure to move the mandrel in the stabiliser. Changes in pressure switch the mandrel between different positions. Such a system is described in EP-A-0190529, in which a differential piston cooperates with a flow restrictor so that, if the fluid pressure rises beyond a low threshold, the piston (or flow restrictor) moves to rapidly and substantially increase the pressure differential across the piston which then drives the mandrel to activate the stabiliser. As a subsidiary feature the mandrel rotates on each stroke because the pads have pins which follow a barrel cam defined around the mandrel, which barrel cam has different steepness ramps so that the pads are extended different amounts. Unintentional variations in fluid pressure might also cause premature activation or deactivation.
GB-A-2263923 discloses a stabiliser control arrangement in which the object is to not be dependent on either fluid pressure or weight on the bit to maintain a stabiliser setting. This is achieved by lifting the drill string to positively disengage the locking mechanism, and then fluid pressure is employed to determine the stabiliser piston position. At the appropriate pressure the drill string is lowered to engage a lock, whereupon subsequent changes in fluid pressure have no effect on stabiliser position.
GB-A-2251444 has essentially the same aims as GB-A-2263923, except that, here, check valves prevent operation or deactivation of the stabiliser pads unless the pressure of the pump fluid exceeds or falls below upper and lower threshold values.
EP-A-0661412 has an arrangement similar to EP-A-190529. The position of a control piston determines the pressure drop across the mandrel which therefore controls the position of the mandrel. The control piston has a barrel cam in which a pin of the housing slides, so that the piston is constrained to follow a course determined by the track. A junction in the track is provided so that, at an intermediate pressure, if the pressure is reversed the pin does not return to its stating point but goes up a branch to a lesser (or greater) extent than its starting point. The stabiliser is activated between upper and lower pressures and that the pressure be taken from one level to an intermediate level whereupon the direction of pressure change is reversed.
GB-A-2314868 describes an arrangement in which the mandrel is hydraulically operated between operative and inoperative positions A first shoulder on the body of the stabiliser in which the mandrel slides has a serrated face. A facing shoulder on the body has a clutch face which is also set Between the two faces is a sleeve which is axially fixed but rotationally freely slidable on the mandrel. On the edge of the sleeve facing the serrated edge of the body is series of knobs to engage the serrations and rotate the sleeve through a small angle when the sleeve is axially pressed against the serrations. On its other edge, it has a series of fingers to engage the clutch face and either catch on ridges of the clutch face, which are provided with stops to prevent further rotation of the sleeve, or they miss the stops and hit a sloping serration of the lower shoulder causing further rotation of the sleeve until its fingers coincide with long slots in the shoulder whereupon the sleeve permits the mandrel to go to its operative position.
Consequently, as pressure is alternated and the mandrel moves back and forth, when it first moves down, for example, it may rest on the ridges of the clutch face and prevent the mandrel from going to its operative position When the pressure is released and the mandrel rises the knohs on the sleeve hit the serrations and turn the sleeve through a small angle; enough so that on the next stroke of the mandrel the fingers on the sleeve do not stay on the ridges. Instead, the fingers slide down the serrations of the clutch face and drop into slots therein. This movement takes the mandrel into its operative position. Finally on the return stroke, when the knobs again contact the serrated face the sleeve again rotates, repeating the cycle.
A problem with this arrangement, and with EP-A-0661412 is that the pressure which activates the stabiliser must be greater, of course, than the return force provided by springs, for example, which springs must themselves be very substantial in order to guarantee deactivation and overcome any jamming tendency which could occur through external pressure on the pistons. Consequently, there is wear on the components which are rotating, or causing the rotation, since they are simultaneously subject to substantial axial loads. Moreover, in the case of GB-A-2314868, because the fingers are the same components which result in rotation of the sleeve, they cannot be as substantial as their loading, particularly in an extended position, would ideally want them to be. Thus they may break.
GB-A-2314868 also discloses application of the mechanism described therein in relation to under reamers.
It is therefore an object of the present invention to provide a down-hole tool activation arrangement which does not suffer firm, or at least mitigates these or other problems.
In accordance with the present invention, there is therefore provided an adjustable down-hole tool comprising
a body having a through bore;
a mandrel axially movable in the body, the mandrel being movable by fluid pressure in the tool against the action of a first return spring between a first, activated position and a second deactivated position;
a sleeve between a shoulder on the body and the mandrel;
at least two sets of castellations, one on one of said shoulder and said mandrel and the other on a facing edge of the sleeve so that, when the castellations are in phase the mandrel is prevented from travelling foam said first to second position and when they are out of phase they interdigitate and the mandrel is not prevented from travelling from said first to second position; and
means to rotate the sleeve relative to the mandrel between said in-phase and out-of-phase positions;
characterised in that
said means comprises a control piston slidable in the mandrel, being movable by fluid pressure in the tool against the action of a second return spring; and in that
one of said piston and mandrel is rotationally fixed with respect to the body.
Preferably, it is said mandrel which is rotationally fixed with respect to the body. Preferably, said control piston is axially slidable with respect to said sleeve and rotationally fixed with respect hereto Preferably, a circumferential barrel cam is defined in one of sad piston and mandrel, a cam follower being disposed in the other thereof, the follower being within the barrel cam so that axial movement of the piston with respect to the mandrel results in corresponding rotation of the piston with respect to the mandrel. In this case, the barrel cam may be shaped so that movement of the piston in one axial stroke and return thereof results in rotation of the sleeve from a said in-phase position to a said out-of-phase position or vice versa. Said castellations are preferably angularly spaced by a phase angle and said stroke and return of the piston results in rotation of the sleeve by said phase angle.
When said mandrel is in said deactivated position, a rise in hydraulic pressure in the tool preferably results in movement of the piston before movement of the mandrel. Said first return spring may be sufficiently stronger than said second return spring to ensure that, when said mandrel is in said deactivated position, a rise in hydraulic pressure in the tool results in movement of the piston before movement of the mandrel. Alternatively, or in addition, a spring loaded detent may be provided between said mandrel and body to retain the mandrel in said deactivated position until a threshold hydraulic pressure has been exceeded, which pressure is greater than that required to move said piston. Said detent may comprise a plunger in a radial bore of the mandrel or body, spring biassed against a lip of the body or mandrel, respectively. Said lip may be of a circumferential groove around the body.
Preferably, the plunger has a through bore connecting the space between the mandrel and body with a space behind the plunger so that hydraulic effects are substantially eliminated. Moreover, there are preferably a plurality of said detents arranged around the circumference of the mandrel. This reduces any moment on the mandrel relative to the body.
The mandrel will usually have a through bore and be scaled to the body abut first and second circumferences, the first being a larger circumference upstream, in terms of fluid flow through the tool, of the second, smaller circumference. Thus hydraulic forces act on the mandrel relative to the body urging the mandrel in a downstream direction.
The piston preferably also has a through bore and is sealed to the mandrel about third and fourth circumferences, the third being a larger circumference upstream, in terms of fluid flow through the tool, of the fourth, smaller circumference. Thus hydraulic forces likewise act on the piston relative to the mandrel also urging the piston in a downstream direction.
Preferably, the piston extends from the mandrel and is sealed to the body. Indeed, the seal between the body and mandrel about said second circumference, and the seal between the piston and mandrel about said fourth circumference, may comprise an integrated seal between the piston and the body.
In said activated position, the bore of the piston preferably engages a plug in the bore of the body to create a flow restriction and consequent back pressure detectable to indicate the position of the tool.
Said tool can be a drill-string stabiliser, in which case said mandrel has wedge surfaces to engage corresponding surfaces on radially disposed pistons slidable in the body, whereby, when the mandrel moves from said deactivated to said activated position, the pistons extend from the body inn sing the working diameter of the stabiliser.